package cnn;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

import java.io.IOException;

public class WordCountApp {
    /**
     * Map: 读取输入的文件内容
     */
    public static class MyMapper extends Mapper<LongWritable, Text, Text, LongWritable> {

        LongWritable one = new LongWritable(1);

        protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
            // 接收到的每一行数据
            String line = value.toString();

            // 按照指定的分割符进行拆分
            String[] words = line.split(" ");
            for (String word : words) {
                // 通过上下文把map的处理结果输出
                context.write(new Text((word)), one);
            }
        }
    }

    /**
     * Reduce: 归并操作
     */
    public static class MyReducer extends Reducer<Text, LongWritable, Text, LongWritable> {

        protected void reduce(Text key, Iterable<LongWritable> values, Context context) throws IOException, InterruptedException {
            long sum = 0;
            for (LongWritable value : values) {
                // 求key出现的次数总和
                sum += value.get();
            }
            // 将最终的统计结果输出
            context.write(key, new LongWritable(sum));
        }
    }

    /**
     * 定义Driver：封装了MapReduce作业的所有信息
     */
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        Configuration configuration = new Configuration();
        // 创建Job，通过参数设置Job的名称

        // 准备清理已存在的输出目录
        Path outputPath = new Path(args[1]);
        FileSystem fileSystem = FileSystem.get(configuration);
        if (fileSystem.exists(outputPath)) {
            fileSystem.delete(outputPath,true);
            System.out.println("output file exists, but is has deleted");
        }

        Job job = Job.getInstance(configuration, "wordcount");

        // 设置Job的处理类
        job.setJarByClass(WordCountApp.class);

        // 设置作业处理的输入路径
        FileInputFormat.setInputPaths(job, new Path(args[0]));

        // 设置map相关参数
        job.setMapperClass(MyMapper.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(LongWritable.class);

        // 设置reduce相关参数
        job.setReducerClass(MyReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(LongWritable.class);

        // 通过Job对象来设置Combiner处理类，在逻辑上和reduce是一样的
        job.setCombinerClass(MyReducer.class);

        // 设置作业处理完成后的输出路径
        FileOutputFormat.setOutputPath(job, new Path(args[1]));

        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}
